1. Field of the Invention
The present invention relates to a mold clamping mechanism of an injection molding machine in which a stationary platen is allowed to rotate so that the parallelism between the stationary platen and a movable platen can be adjusted.
2. Description of the Related Art
In a mold clamping mechanism of an injection molding machine, in general, a stationary platen is fixed to a base frame of an injection molding machine, and the stationary platen and a rear platen are coupled by tie bars. Further, a linear guide for guiding the movable platen in movement is provided on the base frame. The movable platen is moved on the linear guide between the stationary platen and the rear platen directly by a drive source on the rear platen or by means of a toggle mechanism. By doing this, a movable-side mold mounted on the movable platen and a stationary-side mold mounted on the stationary platen are opened, closed, or clamped.
In a well-known mold clamping mechanism of an injection molding machine, a stationary platen fitted with a stationary-side mold is configured to slide on a base frame, and a rear platen is fixed on the base frame.
When a molten material is injected into molds (movable- and stationary-side molds) to form a molded product, the molds are closed and clamped by the mold clamping mechanism. In this case, the stationary- and movable-side molds must be uniformly clamped throughout the surface. To attain this, corresponding surfaces of the stationary and movable platen on which the stationary- and movable-side molds are mounted, respectively, are expected to be parallel to each other. In molding a product that requires high molding accuracy, in particular, the respective opposed surfaces of the stationary platen and the movable platen should be parallel to each other. If this parallelism is low, some molds may be broken.
In a mold clamping mechanism of a type such that a stationary platen is fixed on a base frame, the stationary platen cannot be reoriented in order to adjust the parallelism with a movable platen. In a mold clamping mechanism of a type such that a stationary platen is slidable with respect to a base frame without being fixed to it, on the other hand, a linear guide for guiding a movable platen is extended so that it can also guide the stationary platen in movement. In this known arrangement (Japanese Patent Application Laid-Open No. 3-38319), the stationary platen can be bent uniformly to secure the parallelism between the stationary platen and the movable platen.
In another known arrangement (Japanese Patent Application Laid-Open No. 9-207181), a stationary platen is configured to slide on a base frame so that its upper and lower ends can be freely uniformly deformed by a reaction force of a clamping force, whereby the stationary platen can be prevented from being bent as the clamping force is generated.
In another known arrangement (Japanese Patent Application Laid-Open No. 2000-238100), moreover, a leg portion that is narrower than the space between tie bars is formed protruding from the lower end of a stationary platen, and it is fixed on a base frame. Thus, only the central part of the stationary platen is restricted by the base frame, and the left- and right-hand end portions of the stationary platen are free from thermal expansion.
In still another known arrangement (Japanese Patent Application Laid-Open No. 2001-212857), a stationary platen is mounted on a base frame by a mounting member for movement with respect to the base frame, and the lower part of the stationary platen is allowed to move with respect to the base frame by shock absorbing means, such as a spring, on the mounting member. By doing this, the stationary platen can be prevented from being bent as a clamping force is generated.
In another known arrangement (Japanese Patent Application Laid-Open No. 2004-74454), furthermore, a stationary platen and a rear platen are both located on a base frame for movement with respect to the base frame, and at least one of tie bars that couple the stationary platen and the rear platen is anchored to the base frame. By doing this, the stationary platen can be prevented from being bent as a clamping force is generated.
In a further known arrangement (Japanese Patent Application Laid-Open No. 6-234143), a stationary platen is configured to rotate around a horizontal axis at its central part so that its orientation can be changed. In another arrangement (Japanese Patent Application Laid-Open No. 9-225982), a stationary platen and a rear platen are fixed at their respective horizontal central parts on a base frame, and a position where the stationary platen is fixed to the base frame is slidable. Thus, distortion of the stationary platen can be made vertically symmetric and uniform as a clamping force is generated. Likewise, in still another arrangement (Japanese Patent Application Laid-Open No. 2000-301569), the horizontal central part of a stationary platen is rotatably supported on a base frame, whereby a clamping force can be uniformly applied to the whole surfaces of molds.
Based on the assumption that the stationary platen and the movable platen are parallel, the techniques described in the above eight patent documents are intended to prevent, or equalize, bending of the stationary platen as the clamping force is generated.
In another known arrangement (Japanese Patent Application Laid-Open No. 1-69320), a support is fixed to a leg portion of a movable platen and placed on a guide mounting plate that is fixed to a guide block of a linear movement guide. The guide mounting plate and the movable platen are rotatably coupled together with a pin so that the orientation of the movable platen with respect to its moving direction is adjustable. Thus, the parallelism between the movable platen and a stationary platen can be adjusted.
According to the above patent document, Japanese Patent Application Laid-Open No. 1-69320, the parallelism between the stationary platen and the movable platen is adjusted by reorienting the movable platen with respect to its moving direction. There is an assumption that the stationary platen extends at right angles to the liner movement guide along which it moves, and the orientation of the stationary platen is not adjustable.
In still another known arrangement (Japanese Patent Application Laid-Open No. 2004-276553), a second base frame separate from a base frame that supports a stationary platen and a rear platen is provided with a linear guide, in order to prevent the parallelism between the stationary platen and a movable platen from being ruined as the base frame is bent by the weights of the stationary platen, rear platen, and movable platen. Even if the base frame is bent, therefore, the parallelism between the stationary platen and the movable platen can be maintained with high accuracy by moving the movable platen along the linear guide.